1. Field of the Invention
The present invention relates, in general, to the detection of targets within the human body. The present invention also relates in particular to the detection and localization of microcalcifications in the human breast which may be indicative of the presence of breast cancer.
2. Description of the Prior Art
Breast cancer is often characterized by the presence of calcifications along mammary ducts. These may be detected using X-ray mammography techniques. Unfortunately, mammograms have a number of drawbacks. First, calcifications appear as white/shiny dots in a generally black-and-white background. Fibroglandular tissue, which is normal in breasts, also appears as white which leads to poor contrast in mammographic images. Second, X-ray mammography is an extremely uncomfortable procedure. Third, mammography is an x-ray based modality which involves exposure to harmful ionizing radiation.
An alternative approach, which does lead to better quality images, is to use an MRI. However, MRI may be prohibitively expensive and out of reach for all but a limited number of patients with certain socioeconomic standing.
The concept of using conventional ultrasound imaging technologies to detect calcifications has, in general, been developed prior to this invention. The benefit of using ultrasound is that it is comfortable, affordable, portable, available in a broad number of locations and to a broad range of populations, is less-expensive than MRI and does not impose any harmful radiation such as X-rays. Moreover, in cases with dense breasts, mammograms have proven to have limited utility and therefore, ultrasound is the only method of choice, next to expensive and unaffordable MRI.
United States Published Patent Application 20090247869 describes an approach using ultrasound in conjunction with four or more receiving contact microphones or sensors located on a ring which is positioned on or around the human breast. These sensors are meant to detect sound radiation radiated from an emitting source or multiplicity of emitting sources. A signal emitted from a given location will arrive at each of the receiving sensors at a time determined by the distance between the source and the sensor. Since the speed of sound is constant and finite in different layers of the human breast, the signal will arrive at each of the receiving sensors at different times. If one can precisely estimate the time delays then, in theory, one can locate the position of the emitting source. According to this invention, an ultrasound imaging transducer is used to deliver certain acoustic force to and thereby stimulate a target or multiplicity of targets of acoustic radiation such as microcalcifications. The resulting sound signals, which have markedly different frequencies than the transmitted ultrasound frequencies (i.e., kilohertz response versus megahertz transmitted ultrasound frequencies) are then received by the receiving sensors. Data acquired by the sensors will allow one to determine the location of the microcalcifications in the breast assuming that the relative positions and configurations of the sensors and excitation transducer are known.
The following eight publications and standards are the closest prior art that are relevant to the field of the present invention:                1. United States Published Patent Application No. 20090247869, Rambod, Edmond, et al. Oct. 1, 2009, “Application of Image-based Dynamic Ultrasound Spectrography (IDUS) in detection and localization of breast micro-calcifications.”        2. The Global Positioning System: Theory and Applications, Bradford W. Parkinson, James J. Spilker. 1996.        3. Feasibility of Spread Spectrum Sensors for Location of Arcs on Live Wires, IEEE Sensors, Vol. 5, No. 6, 1445 (2005),        4. Ranging and Data Transmission Using Digital Encoded FM “Chirp” Surface Acoustic Wave Filters, IEEE Transactions on Sonics and Ultrasonics, 20, 2, 190 (1973).        5. IEEE Standard 802.15.4a-2007.        6. Experimental Verification of Real-Valued Orthogonal PN Sequence Applied to Pulse Compression Sonar, Electronics and Communications in Japan, Part I (communications), 75, 3, 72 (2007).        7. Metal Fatigue in Old Aircraft. Flying Rivets. A New Technique that Listens for Cracks in Ageing Aircraft. The Economist. (Aug. 5, 2010).        8. Potential of Coded Excitation in Medical Ultrasound Imaging. Ultrasonics, Vol. 38 (2000) pp. 183-189.        
The prior art requires knowledge of the location of the receiving sensors in an array but provides no explicit method for determining the locations. The prior art describes the use of a sensor array to determine the location of a target or multiplicity of targets based upon the phase delays of signals received from the target or targets but does not describe the format in which the signals should be best generated, acquired, processed, or best interpreted. There has been extensive prior art using coded signals with sharp autocorrelation functions to determine distances in radar, sonar, wire-fault-detection, and direct ultrasound imaging, but there has been no application of coded signals to Image-based Dynamic Ultrasound Spectrography (IDUS), Acoustic Radiation Force Imaging (ARFI), or similar imaging modalities.
A rigid mechanical framework could be used to position the sensors and transducer in fixed, known locations relative to one another but this arrangement is less than ideal in terms of adaptability and the need to maintain contact with the body.
The prior art describes the use of time-of-flight measurements to determine the location of a source of acoustic radiation such as a calcification or other target excited by a modulated ultrasound signal but does not specify a format for the excitation/stimulation signal.